                     (scaled-vector scalar (idx coll))))))
 
 (defn k-harmonic-matrix
+  "returns an N x (2*k) matrix of harmonic series, where N is the
+  length of `coll` and `k` is the number of harmonic terms."
   [freq k coll]
   (let [degree-vector (vec (map inc (range k)))]
     (apply i/bind-columns

  (let [S (:fitted (s/linear-model coll (k-harmonic-matrix freq k coll)))]
    (map #(+ (average coll) %)
         (apply (partial map -) [coll S]))))

;; ## WHOOPBANG :: Collect the short-term drop associated with a
;; ## time-series

  (map #(* scalar %) coll))

(defn harmonic-series
  "returns a vector of scaled cosine and sine series of the same
  length as `coll`; the scalar is the harmonic coefficient"
  [freq coll k]
  (let [pds (count coll)
        scalar (/ (* 2 (. Math PI) k) freq)]
